Disk drives are often used to write data on or to read data from a recording media. A disk drive can include multiple rotating magnetic disks with tracks for storing data and heads to read data from the disks and/or to write data on the disks. The disks are typically arranged in a stacked configuration with the heads arranged in a corresponding stacked assembly referred to as a head stack assembly (HSA). The HSA can be attached to an actuator arm that is typically moved by a voice coil motor (VCM). This arrangement ordinarily allows for positioning of the head to read data from or to write data on an adjacent surface of one of the disks in the stack.
In order to increase the amount of data that can be stored in a given area on the disks, the disk drive industry has been increasing the number of tracks per inch (TPI) on the disks. However, an increased TPI requires more accurate and reliable positioning of the heads over the disks. One approach to improve head positioning is to use a dual stage actuator (DSA). In DSA drives, micro piezoelectric (PZT) actuators can provide a finer actuation for each head in addition to the actuation typically provided by the VCM. Each head in the HSA usually has its own PZT actuator to provide a finer actuation for the head.
In many DSA drives, each PZT actuator includes two PZT elements with a first PZT element of a first polarity adjacent a second PZT element of an opposite polarity. By applying a control voltage across the oppositely polarized PZT elements, it is ordinarily possible to cause one PZT element to contract and the other PZT element to expand, thereby causing movement of the head in a direction perpendicular to the actuator arm.
Typically, the PZT actuators can be arranged in either an in-phase or out-of-phase polarity configuration. In the in-phase configuration, the PZT actuators for each of the heads in the head stack are arranged so that the PZT elements of each PZT actuator have the same polarity on one side of the actuator arm. In this configuration, all the heads in the HSA should move in the same direction when applying the same control voltage.
In the out-of-phase configuration, the PZT actuators are arranged so that the PZT elements of every other PZT actuator have the same polarity on one side of the actuator arm. In this configuration, adjacent heads in the head stack should move in opposite directions when applying the same control voltage. Since each of the in-phase and out-of-phase configurations offers different performance and manufacturing benefits, DSA drives may come in either configuration.
Accordingly, a PZT polarity is usually selected during a setup process for controlling the position of a head based on either an in-phase polarity configuration or an out-of-phase polarity configuration. If the wrong polarity has been selected for a PZT actuator, the head can move in the wrong direction and create head positioning problems during operation of the disk drive.